Add regression test for check_requires_python with no package metadata

[cytolentino]

Add a regression test for check_requires_python for the case where a package has no metadata (see issue #5082).

[BrownTruck]

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[pradyunsg]

@cjerdonek We should add an equivalent regression test for the refactored version if this code.

[cjerdonek]

@cjerdonek We should add an equivalent regression test for the refactored version if this code.

Good find. Will do. Also, I checked the code causing #5082, and the code with the bug is happening higher up the stack inside utils.packaging.get_metadata(), so that still needs to get fixed.

[cjerdonek]

We should add an equivalent regression test for the refactored version if this code.

@pradyunsg I did this here: #6542

[cjerdonek]

This was superseded by PR #6542 linked above, so closing.

Thanks for your work on this @cytolentino, even though this wound up getting fixed a different way.